Susceptibility of multipactor discharges near a dielectric driven by a Gaussian-type transverse rf electric field

Abstract

Multipactor discharge near an rf window is a key limiting factor in high power microwave systems. In this work, we report special features of dielectric multipactor susceptibility under a Gaussian-type waveform as a function of the rf power density of the transverse rf electric field ([Formula: see text]) and normal restoring field ([Formula: see text]) via particle-in-cell (PIC) and multiple particle Monte Carlo (MC) simulations. The MC simulations show that, for a Gaussian waveform of a half peak width ([Formula: see text]), larger than [Formula: see text] with T =  1 ns the rf repetition period, the susceptibility boundary is similar to that of the conventional sinusoidal waveform-driven multipactor, i.e., two inclined lines in the plane of ([Formula: see text]). However, by decreasing [Formula: see text], the susceptibility boundary converts to be a closed curve at [Formula: see text] in the plane of ([Formula: see text]) and further shrinks at [Formula: see text]. PIC simulations with a self-consistent surface and space charge effects also show a reduced [Formula: see text] with increasing [Formula: see text] when [Formula: see text] exceeds a critical value, resulting in a closed curve in the plane of ([Formula: see text]), and the maximum time-averaged [Formula: see text] (multipactor strength) also decreases significantly with further decreasing [Formula: see text] in agreement with MC simulations. Accordingly, the fraction of the rf power density absorbed by the multipactor discharges also decreases nonlinearly with [Formula: see text] from the order of [Formula: see text] to [Formula: see text] (even [Formula: see text]), implying a significant improvement compared to the conventional sinusoidal waveform. The simulations also show that the multipactor susceptibility under a transverse Gaussian-type waveform for different frequencies follows the same scaling law in terms of the ratio of the electric field to the rf repetition rate.